The Question Nobody Ever Explains: Where Does the Kernel End?

A deep dive into where the Linux kernel ends and user space begins. Starting from the observation that all user processes form a tree, the explanation traces back to PID 1 (init), the only process created directly by the kernel. Everything before init is kernel space; everything after is user space. The kernel runs in privileged CPU mode while user applications run in restricted mode, communicating via system calls. Components like desktop environments, display servers, network managers, and shells are all user space processes, not part of the kernel. The init process (often systemd on modern distros) spawns the entire service infrastructure that defines a Linux distribution's personality. A secondary question is also explored: where does the OS end and user applications begin, which turns out to have no clean answer.